1. Field of the Invention
The present invention relates to a developing device, a process cartridge, and an electrophotographic image forming apparatus, which include developer-amount detecting means capable of successive detection of the residual amount of a developer.
In this specification, the term xe2x80x9celectrophotographic image forming apparatusxe2x80x9d refers to a structure that uses an electrophotographic image-forming system to form an image on a recording medium. Examples of the electrophotographic image forming apparatus include electrophotographic copying machines, electrophotographic printers (such as laser beam printers and LED printers), facsimile machines, and word processors.
Also, the term xe2x80x9cprocess cartridgexe2x80x9d refers to a cartridge into which at least one of charging means, developing means, and cleaning means and an electrophotographic photosensitive drum are integrally formed and which is detachably mountable to an electrophotographic image forming apparatus main body. In particular, the term xe2x80x9cprocess cartridgexe2x80x9d also refers to a cartridge into which at least the developing means and the electrophotographic photosensitive drum are integrally formed and which is detachably mountable to the electrophotographic image forming apparatus main body.
2. Related Background Art
Up to now, an electrophotographic image forming apparatus using an electrophotographic image forming process has adopted a process-cartridge system in which an electrophotographic photosensitive member and process means for acting on the electrophotographic photosensitive member are integrally formed into a cartridge, and the cartridge is detachably mountable to an electrophotographic image forming apparatus main body. The process-cartridge system enables a user per se to perform the maintenance of the apparatus without relying on a service person, thereby making it possible to improve the operability remarkably. For that reason, the process-cartridge system is widely employed in electrophotographic image forming apparatuses.
Also, in such an electrophotographic image forming apparatus of the process-cartridge system, it is necessary that the user per se exchange the cartridges. Therefore, in order to inform the user that a developer is consumed, some of the electrophotographic image forming apparatuses are equipped with developer-amount detecting means. Examples of the developer-amount detecting means include one using a system in which a change in capacitance among plural electrodes arranged within the process cartridge is detected, to thereby detect the developer amount.
Some structures of the electrodes have plural electrode plates arranged so as to be opposed to each other in positions to which a developer can be admitted.
FIG. 2 is a cross sectional view showing an example of the conventional process cartridge having the developer-amount detecting means. Developing means 52 of a process cartridge 51 is provided with a first electrode 53 and a second electrode 54 which serve to detect the developer amount. The first electrode 53 and the second electrode 54 are arranged in a position to which toner as the developer can be admitted, and the capacitance between the electrodes is detected to thereby detect a toner amount successively.
FIG. 3 is a side view of the process cartridge 51. On a side surface of the process cartridge 51, an input contact 55 and an output contact 56 are provided. The input contact 55 is electrically connected to the first electrode 53 and serves to receive an input voltage from the image forming apparatus main body. The output contact 56 is electrically connected to the second electrode 54 and serves to send an output voltage corresponding to the toner amount to the image forming apparatus main body.
FIG. 4 shows an electrical circuit of the developer-amount detecting means.
A developer-amount detecting circuit 60 is composed of a detecting portion 64, a developing-bias circuit 61, a control circuit 62, and an amplifying circuit 63. The detecting portion 64 is composed of the first electrode 53, the second electrode 54, and a developing sleeve 57, and induces a capacitance in order to detect the toner amount. The detecting portion 64 is provided to the process cartridge 51.
On the other hand, the developing-bias circuit 61, the control circuit 62, and the amplifying circuit 63 are provided to the image forming apparatus main body.
The process cartridge 51 includes a developing-bias electrode 57a electrically connected to the developing sleeve 57. The image forming apparatus includes an electrical contact 65 electrically connected to the developing-bias circuit 61. When the process cartridge 51 is mounted to the image forming apparatus, the developing-bias electrode 57a and the electrical contact 65 that is provided to the image forming apparatus are electrically connected to each other, and a developing-bias voltage is applied to the developing sleeve 57 from the developing-bias circuit 61 of the image forming apparatus via the electrical contact 65 and the developing-bias electrode 57a. 
Also, provided on a side surface of a frame of the process cartridge 51 are the external input contact 55 and the external output contact 56, which are to be electrically connected to the image forming apparatus. When the process cartridge 51 is mounted to the image forming apparatus main body, the external input contact 55 and the external output contact 56 contact an electrical contact 58 and an electrical contact 59 which are provided to the image forming apparatus, respectively.
The detecting portion 64 functions as an impedance element. The first electrode 53, serving as an input side electrode that is one electrode of the detecting portion 64 is connected to the developing bias circuit 61 functioning as developing-bias application means via the developing-bias electrode 57a. 
The second electrode 54, serving as an output-side electrode that is the other electrode of the detecting portion 64, is connected to the control circuit 62. In the above structure, the first electrode 53 is connected to the developing-bias circuit 61 via the external input contact 55 and the electrical contact 58 of the apparatus main body, and the second electrode 54 is connected to the control circuit 62 via the external output contact 56 and the electrical contact 59 of the apparatus main body.
As described above, the process cartridge and a developing device, which include the developer-amount detecting means are provided with an external input contact and an external output contact. The external input contact serves to receive an input voltage to be applied to developer-amount detecting electrodes from the image forming apparatus main body. The external output contact serves to send an output voltage corresponding to the capacitance between the detecting electrodes to the image forming apparatus main body. On the other hand, the image forming apparatus main body is provided with electrical contacts which are electrically connected to the above-discussed external contacts when the process cartridge or the developing device is mounted to the image forming apparatus main body.
As described above, it is necessary to provide the process cartridge or the developing device and the image forming apparatus main body with the external input contact and the external output contact. Thus, there is a fear that the contacts have complicated structures resulting in obstacles to the downsizing of the apparatus and the reduction in costs. Further, during the progress in downsizing the apparatus, there is also a fear that the degree of freedom in the arrangement of the contacts is reduced in order to achieve the complicated structures of the contacts.
The present invention has been made in order to solve the above-mentioned problem.
An object of the present invention is to provide a developing device, a process cartridge, an electrophotographic image forming apparatus using a developing device, and an electrophotographic image forming apparatus to which a process cartridge is detachably mountable, in which a bias that is applied to a developing sleeve for developing a latent image formed on an electrophotographic photosensitive member and an electrode serving to detect the residual amount of a developer used for developing the latent image on the developing sleeve can be received from an image forming apparatus main body by common electrical contacts.
Another object of the present invention is to provide a developing device, a process cartridge, an electrophotographic image forming apparatus using a developing device, and an electrophotographic image forming apparatus to which a process cartridge is detachably mountable, in which, while maintaining a function to detect a developer residual amount, the number of electrical contacts for receiving a bias from an image forming apparatus main body can be reduced.
Another object of the present invention is to provide a developing device, a process cartridge, an electrophotographic image forming apparatus using a developing device, and an electrophotographic image forming apparatus to which a process cartridge is detachably mounted, in which the degree of freedom is improved in an arrangement of the electrical contacts for receiving a bias from an image forming apparatus main body upon arranging the electrical contacts.
Another object of the present invention is to provide a developing device, a process cartridge, an electrophotographic image forming apparatus using a developing device, and an electrophotographic image forming apparatus to which a process cartridge is detachably mountable, in which downsizing is achieved.
Another object of the present invention is to provide a developing device, a process cartridge, an electrophotographic image forming apparatus using a developing device, and an electrophotographic image forming apparatus to which a process cartridge is detachably mountable, in which a reduction in costs is achieved.
Another object of the present invention is to provide a developing device, a process cartridge, an electrophotographic image forming apparatus using a developing device, and an electrophotographic image forming apparatus to which a process cartridge is detachably mountable, in which a reliability of electrical connection is improved.
Another object of the present invention is to provide a developing device, a process cartridge, an electrophotographic image forming apparatus using a developing device, and an electrophotographic image forming apparatus to which a process cartridge is detachably mountable, in which a bias that is applied to a developing sleeve for developing a latent image formed on an electrophotographic photosensitive member and an electrode serving to detect the residual amount of a developer used for developing the latent image on the developing sleeve can be received from an image forming apparatus main body by common electrical contacts.
These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.